Radeon HD 7970: A Holiday Surprise That You Can't Buy
Leading into December, we didn’t really expect to see a next-generation graphics card in the 31 days before 2012. In fact, even mid-month, after we’d already been briefed, the plan was to launch in January. Windows 8 and its accompanying DirectX 11.1 API update aren’t expected for months still, and today’s high-end graphics cards are well-equipped to handle modern games. Despite the fact that AMD purportedly stopped production of its Radeon HD 6990 months ago, we were worried that rumors of poor 28 nm yields at TSMC meant there was no way a new GPU could be readied in time.
When AMD moved its launch date up to today, we were even more bowled over. The official line from AMD was that “After collecting feedback from our partners and evaluating our overall readiness…we believe this new date allows us to get ahead of the Christmas season rush and CES.” Getting ahead of the Christmas rush by launching 72 hours before the big day is a tough line to swallow, especially after a follow-up confirming that cards won't be shipping until January 9th. The unfortunate result is that a lot of AMD’s software partners were unprepared to provide us with the applications needed to properly test the GPU’s new features. So, this article officially goes down as a preview, rather than a review. We will, of course, follow up when all of the proper tools are available for testing.
Meet Radeon HD 7970
Regardless of whether or not it’s ready for the world, or the world is ready for it, AMD’s Radeon HD 7970 is up and running in the Tom’s Hardware lab. This card is no minor revision of the Radeon HD 6000 series. The company’s ”Southern Islands” architecture was re-designed from the ground up with a long list of new features and capabilities, including DirectX 11.1 compatibility. Composed of 4.31 billion transistors etched on a 28 nm process, the flagship Tahiti GPU sports about 160% of the Cayman design’s reported transistor count. However, adopting the latest lithography node allows AMD to cram that extra complexity into a 365 mm² die, which is smaller than its predecessor’s 389 mm² surface area.
Before we delve into the major architectural redesign, let’s have a closer look at the new card’s specifications compared to its competition.
| Header Cell - Column 0 | Radeon HD 7970 | Radeon HD 6970 | Radeon HD 6990 | GeForce GTX 580 |
|---|---|---|---|---|
| Stream processors | 2048 | 1536 | 3072 | 512 |
| Texture Units | 128 | 96 | 192 | 64 |
| Full Color ROPs | 32 | 32 | 64 | 48 |
| Graphics (Shdr) Clock | 925 MHz | 880 MHz | 830 MHz | 772 (1544) MHz |
| Texture Fillrate | 118.4 Gtex/s | 84.5 Gtex/s | 159.4 Gtex/s | 49.4 Gtex/s |
| Memory Clock | 1375 MHz | 1375 MHz | 1250 MHz | 1002 MHz |
| Memory Bus | 384-bit | 256-bit | 2x 256-bit | 384-bit |
| Memory Bandwidth | 264 GB/s | 160 GB/s | 160 GB/s | 192.4 GB/s |
| Graphics RAM | 3 GB GDDR5 | 2 GB GDDR5 | 2 GB GDDR5 | 1.5-3 GB GDDR5 |
| Die Size | 365 mm2 | 389 mm2 | 2 x 389 mm2 | 520 mm2 |
| Transistors (Billion) | 4.31 | 2.64 | 5.28 | 3 |
| Process Technology | 28 nm | 40 nm | 40 nm | 40 nm |
| Power Connectors | 1 x 8-pin, 1 x 6-pin | 1 x 8-pin, 1 x 6-pin | 2 x 8-pin | 1 x 8-pin, 1 x 6-pin |
| Maximum power (TDP) | 250 W | 250 W | 375 W | 244 W |
| Price | $549 MSRP | $340-$380 (Newegg) | $700-$750 (EOL) | $500-$530 (1.5 GB)$590-$730 (3 GB) |
This product boasts notable advantages over the Radeon HD 6970, with 33% more stream processors and texture units, and a 65% net memory bandwidth increase thanks to its 384-bit memory bus. The only specifications that these cards share are 32 ROPs and a 250 W TDP. Based on those figures alone (and the fact that this is apparently going to be a $550 card), we’d expect the Radeon HD 7970 to decimate the 6970, edge past the GeForce GTX 580, and fall behind AMD’s Radeon HD 6990. There’s frankly a lot more to this story than gaming performance, though, and we’ll get to that in an in-depth exploration of AMD’s new Graphics Core Next architecture.
But first, we’ll share what we know about the Radeon HD 7000 series. Despite rumors to the contrary, all of the 28 nm Radeon 7000 series GPUs, previously code-named Southern Islands, are based on the Graphics Core Next architecture. That includes the Radeon HD 7700 series (Cape Verde Core), 7800 series (Pitcairn), and 7900 series (Tahiti), at the very least. AMD may include some 40 nm products under the 7000-series umbrella, and those would employ rebranded VLIW4/5 architectures.
The Southern Islands-based cards share the same features and abilities, which is good news. Here is a slide showing the placement of new product families relative to the Radeon HD 6000 series:
As you’ll see in our tests, the Radeon HD 7900 series appears to perform as its position in the deck would suggest. Note the Q1, 2012 expected date and the unnamed dual-GPU product at the top of the food chain.
With the relative performance of Radeon HD 7000-series cards established by AMD’s marketing department, let’s have a look at the family’s unique features. We’ll start with the basics: the Southern Islands architecture.
